Sump pump cavitating like crazy! Help Please...

[drewread]

Hello all!

My sump pump is cavitating like mad and it is driving me nuts... I have tried three different pumps and changed some of the plumbing. Any help would be appreciated.

Symptoms: Major cavitation noise at pump and many microbubbles entering tank.

You can see what my plumbing looks like via:

http://www.andrewread.com/PersonalPages/plumbing.html

I have to restrict my pump output to 1/2 before the cavitation stops (at 'full bore' there is an immense amount of cavitation!)

I am currently using a MagDrive36 (3600GPH) and have tried a MagDrive1800 and a Little Giant 4MD. All pumps were brand new.

There is no 'whirlpooling' in the sump.

Any help would be appreciated.

 

[Anonymous]

the towel? there are no leaks are there?

just ruling out a venturi introducing air in the inlet.

also, the tee you have installed off the discharge shouldn't be "bullheaded" like that. i doubt that is the problem, but worth consideration.

 

[drewread]

The towels are just there because I changed the soft link to a hard link... no leaks... unless they are so small that water can't get out but air can get in (unlikely I think!

Which 'T' are you talking about? there are two... one to calcium reactor or for water changes and one to tank returns... Either way this should only restrict the pumps output more not cause cavitation...

 

[Anonymous]

Which 'T' are you talking about? there are two...

the second one off the discharge.

Either way this should only restrict the pumps output more not cause cavitation...

you said yourself that throttling the above valves increased and decreased cavitation, that is because flow was altered. the flow hitting a diversion area like that tee will cause inconsistencies in the flow. if a centrifugal pump is restricted enough it will cavitate.

i am not saying this is your problem, i am just saying that the way that tee is installed is improper piping practices and may be the problem. i, like you, don't find it likely.

there wasn't a bulk of critters living in the suction line you pulled apart, was there?

 

[drewread]

I understand what you are saying but the more I restrict it the less cavitation I get (on the output side NOT the input side) so I really don't think this is a problem... How do you suggest I divert it?

Also, what do you mean by critters?

 

[cal91666]

Cavitation of a pump is generally caused by air being introduced on the suction side or a restriction on the suction side.

 

[Anonymous]

If you shut down the output, you will get no cavitation. Whether there is a tee in the output or 20 tees in the output won't effect it. Cavitation occures when the input side of the pump is restricted compared to the output. To reduce or eliminate it, restrict the output.

 

[cal91666]

IMHO looking at your pictures if I'm seeing them correctly I'm seeing a partition in the sump which is very close to the inlet bulkhead fitting.... possible restriction. Valve between sump and pump is a possible restriction and also check the orings in the unions for leaks allowing air to be introduced.

 

[drewread]

Are you talking about the third baffle from the left? If so this one has already been removed ( all that remains is some traces of the silicone)... as I thought that that was the problem.... however it doesn't seem to have been...

I am fairly certain that there are no air leaks on the intake side...

Keep the ideas flowing (pardon the pun!) they are great...

 

[cal91666]

I work with hydraulics all day everyday and the same principal should apply here. I think I would start by removing the valve between the sump and pump and see what happens. Unless I'm missing something that is beyond my training you problem is going to be on the suction side and the valve is the only restriction present.

 

[drewread]

Actually... I have also tried that as well (removing the valve)... a rather messy project I assure you..

That didn't seem to be the problem either as the only thing that I had there was a pipe to the pump... and I still had the problem...

Now you know why I seem so frustrated!!

 

[cal91666]

Are you getting many/any bubbles from say a skimmer return or anything in the sump that might make its way to the inlet?

 

[drewread]

I have a bright light on under the tank now and am looking at that... I had always assumed no... but there seems to be actually quite a few making it there...

I am making another baffle or two now.. and also trying to stop skimmer bubbles from getting back to my sump... not easy as you know... any suggestions on this one?

 

[cal91666]

You probably just found your problem. The micro bubbles will cavitate a pump. Try to adjust your skimmer so that it introduces as few bubbles as possible into the sump and you might want to also try a sponge between the baffles to help control some of the bubbles getting into the inlet of the pump.

 

[drewread]

yea... Looking into that now... I never thought I had any... but they are so small that without a bright light you can't even see them! It will drive me crazy until I get that sorted out... and even craizer if that isn't the problem..!

 

[Anonymous]

Cavitation of a pump is generally caused by air being introduced on the suction side or a restriction on the suction side.

i agree, generally.

Whether there is a tee in the output or 20 tees in the output won't effect it.Cavitation occures when the input side of the pump is restricted compared to the output.

CW,
unstable head pressures most certainly can cause cavitation. maybe i will ask for your credentials on this one :wink:

drewread,
FWIW, i think the bubbles could cause it as well.

and what i meant by "critters" was any encrusting squirts or coralline kind of stuff that could be restricting the flow on the inlet side.

hope you have gotten to the cause of your troubles

 

[drewread]

;c) Haven't quite got it licked yet... bubbles are WAY down in the sump... 3 temporary baffles and some skimmer tuning (I will eventually plumb the skimmer returns right back in to the first chamber of my sump through the splash wall)... I personally think it will be 'impossible' to remove all the bubbles from the water column inside the sump...when it goes over one baffle it creates more bubbles again...

I will try to see if adding a Y and some smooth curves will fix the problem if you think that 'backpressure' which is what I assume is being created will cause the cavitation at 'full bore'... I would hate to replumb that all again and find that that wasn't the problem... :c( but one can only experiment!

Off to sleep for tonight...

 

[cal91666]

Your baffles should not be so high as to cause a "waterfall" over them. My suggestion would be this: 1st baffle water goes under, remember bubbles will rise, 2nd baffle water goes over, but isn't so high as to cause a "waterfall", 3rd baffle water goes under, again giving bubbles a second chance to rise and stay away from inlet on pump. I still believe your problem is on your suction/inlet side. Good luck to you. I'll be away for a few days so I'll check back in Sunday hoping to read you have solved your problem.

 

[drewread]

FYI - I have tried submerging the MagDrive36 in the sump to see if there is a problem with my connection to the bulkhead... and the only change is that it is slightly quieter... probably because it is underwater...

 

[Clark]

Is that a check valve coming out of the outlet of the pump? or just a coupling? I can't tell..

If it is a check valve, move the check valve up the line closer to the tank..see if that fixes the problem.